The epithelial lining of the mammalian intestinal tract develops from a simple tube of embryonic endoderm through a complex process of changes in morphology and gene expression. However, little is known about the molecular mechanisms that direct and integrate the developmental transitions leading to the mature configuration of the adult intestinal epithelium. Using expression cloning, our laboratory has identified a cDNA encoding a protein that binds with high affinity to, and activates transcription of, an intestine-specific DNA regulatory element. The protein encoded by this cDNA is a member of the caudal-related homeodomain family of transcription factors (Cdx); homeodomain proteins are of central importance in many organisms for developmental processes throughout embryogenesis and organogenesis. This proposal is based on the hypothesis that Cdx genes are important for directing development and differentiation of the mouse intestinal epithelium. Therefore, the overall goal of this project is to investigate the role of Cdx genes in intestinal organogenesis and differentiation. To achieve this goal the specific aims of this proposal are: l) To characterize the developmental and cellular patterns of expression of Cdx genes in the intestine. The expression of Cdx-1 and Cdx-2 genes will be examined in the developing mouse intestinal tract using in situ hybridization and immunohistochemistry. 2) To examine the functional role of Cdx genes in differentiation of the intestinal epithelium using intestinal cell lines. Several cell lines that have been derived from intestinal tissue or colon carcinomas, as well as the F9 teratocarcinoma cells line, will be used to study both the gain of function and loss of function of Cdx genes. 3). To examine the functional role of Cdx genes in development of the mouse digestive tract using transgenic mice. Gain of function and loss of function studies will be performed in transgenic mice using the promoter of the villin gene to express constructs that contain coding regions for Cdx genes and the effect on development will be evaluated. This strategy will allow an assessment of the effect of premature and ectopic expression of Cdx genes in the intact mouse. The experiments described in this proposal will elucidate the role of Cdx homeobox genes in intestinal differentiation and development.